The invention relates to a capacitance proximity switch intended primarily for manual operation by a human, but also capable of detecting objects in proximity thereto, such as moving machine parts or production items.
There is substantial body of prior art pertaining to capacitance proximity switches, including the U.S. Pat. No. 3,761,736 wherein is disclosed a differential capacitance proximity switch in a bridge circuit having self balancing capability, and the U.S. Pat. No. 3,723,885 disclosing a digital circuit capacitance proximity switch.
Also in the U.S. Pat. No. 3,796,895 is disclosed a piezoelectrically controlled solid state switching circuit using a commercially available MOSFET logic unit, having inherent high input impedance and consequent low energy dissipation.
The above and other prior art patents disclose devices requiring the use of discrete components and devices. What is required is a proximity switch device which lends itself to economical mass production without any sacrifice in performance or in reliability.